Lawful Interception and Data Retention of communications is used to intercept speech calls made or received by persons suspected of criminal activities. In governments around the world, various law enforcement agencies may have the right to authorize this interception/retention in their respective jurisdictions.
FIG. 1 is part of the prior art and discloses an Intercept Mediation and Delivery Unit IMDU, also called Intercept Unit. The IMDU is a solution for monitoring of Interception Related Information IRI and Content of Communication CC for the same target. The different parts used for interception are disclosed in current Lawful Interception standards (see 3GPP TS 33.107 and 3GPP TS 33.108—Release 8). A Law Enforcement Monitoring Facility LEMF is connected to three Mediation Functions MF, MF2 and MF3 respectively for ADMF, DF2, DF3 i.e. an Administration Function ADMF and two Delivery Functions DF2 and DF3. The Administration Function and the Delivery Functions are each one connected to the LEMF via standardized handover interfaces HI1-HI3, and connected via interfaces X1-X3 to an Intercepting Control Element ICE in a telecommunication system. Together with the delivery functions, the ADMF is used to hide from ICEs that there might be multiple activations by different Law Enforcement Agencies. Messages REQ sent from LEMF to ADMF via HI1 and from the ADMF to the network via the X1_1 interface comprise identities of a target that is to be monitored. The HI1 interface is thus used to set the interception orders in the operator network. The Delivery Function DF2 receives Intercept Related Information IRI from the network via the X2 interface. DF2 is used to distribute the IRI to relevant Law Enforcement Agencies LEAs via the HI2 interface. The Delivery Function DF3 receives Content of Communication CC, i.e. speech and data, on X3 from the ICE. Requests are also sent from the ADMF to the Mediation Function MF2 in the DF2 on an interface X1_2 and to the Mediation Function MF3 in the DF3 on an interface X1_3. The requests sent on X1_3 are used for activation of Content of Communication, and to specify detailed handling options for intercepted CC. In Circuit Switching, DF3 is responsible for call control signaling and bearer transport for an intercepted product. Intercept Related Information IRI, received by DF2 is triggered by Events that in Circuit Switching domain are either call related or non-call related. In Packet Switching domain the events are session related or session unrelated. In Packet Switching domain the events are session related or session unrelated.
For the activation of Intercept Related Information IRI, the message sent from the ADMF to the DF contains the target identity, which can be one of the following: the IMSI, MSISDN or IMEI codes commonly associated to a mobile phone subscription. Moreover, the message sent from the ADMF to the DF contains the address for delivery of IRI (i.e. the LEMF address), which subset of information shall be delivered, a DF2 activation identity, which uniquely identifies the activation for DF2 and is used for further interrogation or deactivation, respectively. Furthermore, the message sent from the ADMF to the DF also contains the IA and the warrant reference number, if required by national option.
Intercept Related Information events are generated at various moments, particularly when a call is initiated or ended, or for all supplementary services during a call and also for information which is not associated to a call. That is, there are call-related IRI events and non call-related IRI events. In any case, whenever an IRI event occurs which is originated by or directed to a mobile subscriber, the Intercepting Control Element ICE in the network sends the relevant data to the DF2 for them to be delivered to the LEMF.
To assure correlation between the independently transmitted Content of Communication CC and Intercept Related Information IRI of an intercepted call, the following parameters are used: Lawful Interception Identifier LIID, Communication Identifier CID and CC Link Identifier CCLID. Law enforcement provides an alphanumeric string, the Case Identity to identify a particular surveillance. A case identity may be assigned to a Monitored Object through a command.
The present digital cellular systems support a huge number of codec types. As a result, in order to allocate transcoders for a call inside the network and to select appropriate codec type inside the User Equipments, signaling procedures are defined to convey the codec type selected for a call to all affected nodes. Codec negotiation capabilities are defined to enable the selection of a codec type supported in all the affected nodes, that is, to resolve codec mismatch. This codec negotiation maximizes the chances of operating in compressed mode end-to-end for mobile-to-mobile calls. To allow transport of information in a compressed way in transmission networks, these networks make use of the transport-independent call control protocol, which provides means for signaling codec information, negotiation and selection of codecs end-to-end. Different codec negotiation procedures are described in standard 3GPP TS 23.153 Release 8. These procedures occur at call setup or in case of modifications, that is modification of selected codec, modification of available codec list, and mid-call codec negotiation. In all cases, both the originating and terminating MSC Server (which comprises the Intercepting Control Element ICE) are aware of the selected codec for the concerned call.
The AMR-WB (Adaptive Multi-Rate WideBand) speech codec algorithm is standardized both in 3GPP and in ITU-T with nine different encoding bit rates, ranging from 6.60 kbps up to 23.85 kbps. For speech telephony services, five of these nine modes are allowed in 3GPP, that is 15.85, 14.25, 12.65, 8.85 and 6.60 kbps. The frequency span for the analogue speech signal for AMR-WB ranges from 100 Hz to 7000 Hz, thus providing excellent speech quality due to a wider speech bandwidth compared to narrowband speech codecs which in general are optimized for wireline quality of 300 to 3400 Hz. FIG. 2 schematically shows the difference in spectrum range between AMR narrowband and wideband codecs. In AMR-WB, the extended lower spectrum brings volume and quality, while the extended higher spectrum brings clarity and transparency to the speech signal.
In the existing systems for Lawful Interception and Data Retention, a Law Enforcement Monitoring Facility LEMF has no information about whether an intercepted speech call is an end-to-end call using an AMR-WB codec, where a wider baseband spectrum is used by the parties in the call. This is of particular importance because if the Call Content is delivered over HI3 interface to a simple ISDN DSS1 terminal, the extended wideband frequency range is completely missed at the LEMF site.
This could represent a problem because malicious information could be transported over the wideband spectrum in the main call that would be completely missed over the monitoring leg. For instance, a criminal could make use of Morse signalling by means of acoustic signals between 3400 Hz and 7000 Hz frequency, or apply a frequency modulation of the narrowband speech at around 5200 Hz. Should this occur, the LEMF would miss important pieces of communication in the intercepted call, thus jeopardizing the task of completely monitoring the information exchanged via the operator network by a person suspected of criminal activities.
The problem at hand is thus how to detect and extract information possibly transported over the wideband spectrum in a end-to-end call involving a target who is a subject of lawful interception and or data retention due to a judicial warrant.